Electric brake actuator, and brake system for vehicle

ABSTRACT

A motor cylinder device ( 16 ) is configured with a cylinder mechanism ( 76 ) provided with first and second slave pistons that are displaced along a hydraulic pressure chamber; an electric motor ( 72 ) for driving first and second slave pistons; and an actuator housing ( 75 ) formed separable from the cylinder mechanism ( 76 ), wherein the actuator housing houses a gear mechanism for transmitting a rotational driving force of the electric motor ( 72 ), and a conversion mechanism for converting the rotational driving force transmitted through the gear mechanism, into a linear movement and transmitting the linear movement to the piston.

TECHNICAL FIELD

The present invention relates to an electric brake actuator, for example, built in a brake system for a vehicle, and a brake system for a vehicle.

BACKGROUND ART

Conventionally, as a brake mechanism for a vehicle, for example, servo units using a negative pressure booster or a hydraulic booster are known. As this kind of a servo unit, in recent years, electric servo units using an electric motor as boosting sources have been disclosed (for example, see Patent Document 1).

The electric servo unit disclosed in this Patent Document 1 is configured as an integrated unit including a main piston that is advanced and retreated by operation of a brake pedal, a cylindrical booster piston that is fitted outside the main piston relatively displaceably, and an electric motor for moving forward and backward the booster piston.

In this case, the main piston and the booster piston are arranged as the pistons for a master cylinder, and the respective front ends are located in the pressure chamber of the master cylinder. Therein, an input thrust force applied to the main piston from a brake pedal and a booster thrust force applied from an electric motor to the booster piston generate a brake hydraulic pressure in the master cylinder.

BACKGROUND ART DOCUMENT Patent Document

Patent Document 1: JP2010-23594 A

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, for the electric servo unit disclosed by Patent Document 1, a fluid pressure generation mechanism for generating a fluid pressure by a force that is input from the brake pedal and another fluid pressure generation mechanism for generating a fluid pressure by a force that is input from the electric motor are integrally configured. Consequently, the entire device size tends to be large, and a problem is caused that the device lacks versatility in manufacturing.

The present invention has been developed in the above-described point of view, and aims to provide an electric brake actuator and a brake system for a vehicle, wherein downsizing of the entire device and improvement in versatility are possible.

Means for Solving the Problems

To achieve the aim the present invention provides an electric brake actuator for generating a brake hydraulic pressure, based on an electric signal according to a braking operation, comprising: a cylinder provided with a piston that is displaced along a hydraulic pressure chamber: an electric motor configured to drive the piston; and an actuator housing formed separable from the cylinder, wherein the actuator housing houses a gear mechanism configured to transmit a rotational driving force of the electric motor, and a conversion mechanism configured to convert the rotational driving force transmitted through the gear mechanism, into a linear movement and transmit the linear movement to the piston.

According to the present invention, by constructing the electric brake actuator by three members that are a cylinder, an electric motor, and an actuator housing, a desired brake pressure can be generated with a simple structure, the entire device can be downsized, and the versatility can be improved.

In addition, the present invention provides the actuator housing including a mount portion configured to be mounted and to support the electric brake actuator.

According to the invention, the actuator housing can be stably supported through the mount portion provided at the actuator housing, and the actuator housing can be easily fitted to another member, for example, the vehicle body frame. In this case, by forming the mount portion, for example, by a first boss portion and a second boss portion protruding toward the left and right sides along a direction substantially perpendicular to the axial line of the cylinder, and a third boss portion protruding downward with respect to the cylinder, it is possible to further stably support the actuator housing at three points.

The present invention provides the electric brake actuator, wherein the actuator housing is configured to be divisible in two on a plane substantially orthogonal with an axial line of the cylinder as a dividing plane.

According to the invention, the fastening direction by a plurality of fastening members, such as bolts, can be set parallel to the axial line direction of the cylinder. The fitting task of the actuator housing with a divided structure can thereby be easily carried out.

The present invention provides a brake system for a vehicle, generating a brake hydraulic pressure based on an electric signal according to a braking operation, comprising: a cylinder provided with a piston that is displaced along a hydraulic pressure chamber: an electric motor configured to drive the piston; and an actuator housing formed separable from the cylinder, wherein the actuator housing houses a gear mechanism configured to transmit a rotational driving force of the electric motor, and a conversion mechanism configured to convert the rotational driving force transmitted through the gear mechanism, into a linear movement and transmit the linear movement to the piston.

According to the invention, it is possible to obtain a vehicle brake system provided with a motor cylinder device that is capable of generating a desired brake pressure with a simple structure and enables downsizing of the entire device and improvement in the versatility.

Advantageous Effect of the Invention

According to the present invention, it is possible to obtain an electric brake actuator and a brake system for a vehicle, wherein downsizing of the entire device and improvement in versatility are possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic configuration of a vehicle brake system in which a motor cylinder device in an embodiment according to the invention is built;

FIG. 2 is a perspective view of the motor cylinder device shown in FIG. 1;

FIG. 3 is a side view of the motor cylinder device;

FIG. 4 is an exploded perspective view of the motor cylinder device;

FIG. 5 is an exploded perspective view of a driving force transmission section of the motor cylinder device;

FIG. 6 is an exploded perspective view of a cylinder mechanism of the motor cylinder mechanism;

FIG. 7 is a perspective view of the motor cylinder device in a view from below; and

FIG. 8 is a perspective view showing a state that the motor cylinder device is fixed to a vehicle body frame through a mount portion.

EMBODIMENT FOR CARRYING OUT THE INVENTION

An embodiment according to the present invention will be described below, referring to the drawings, as appropriate. FIG. 1 shows a schematic configuration of a vehicle brake system in which a motor cylinder device in the present embodiment according to the invention is built.

A vehicle brake system 10 shown in FIG. 1 includes two brake systems that are a brake system of a by-wire type for a general operation, which operates a brake by transmitting an electric signal and a brake system of a conventional hydraulic type for fail-safe, which operates a brake by transmitting a hydraulic pressure.

Accordingly, as shown in FIG. 1, the vehicle brake system 10 basically has a structure in which there are individually provided an input device 14 for inputting an operation of a brake pedal 12 upon operation by an operator, a motor cylinder device 16 for controlling the brake hydraulic pressure, and a vehicle stability assist device 18 (hereinafter referred to as the VSA device 18, VSA: trade mark) for assisting stabilization of vehicle behavior.

These devices, namely, the input device 14, the motor cylinder device 16, and the VSA device 18 are connected by hydraulic passages formed by a tube material, for example, a hose or a tube. Further, as a by-wire brake system, the input device 14 and the motor cylinder device 16 are electrically connected by a harness, not shown.

Regarding the hydraulic passage, a connection point A1 in FIG. 1 being defined as a reference, a connection port 20 a of the input device 14 and the connection point A1 are connected by a first piping tube 22 a. Further, an output port 24 a of the motor cylinder device 16 and the connection point A1 are connected by a second piping tube 22 b. Further, an inlet port 26 a of the VSA device 18 and the connection point A1 are connected by a third piping tube 22 c.

With another connection point A2 in FIG. 1 as a reference, another connection port 20 b of the input device 14 and the connection point A2 are connected by a fourth piping tube 22 d. Further, another output port 24 b of the motor cylinder device 16 and the connection point A2 are connected by a fifth piping tube 22 e. Still further, another inlet port 26 b of the VSA device 18 and the connection point A2 are connected by a sixth piping tube 22 f.

The VSA device 18 is provided with a plurality of outlet ports 28 a to 28 d. The first outlet port 28 a is connected, by a seventh piping tube 22 g, with a wheel cylinder 32FR of a disk brake mechanism 30 a provided at the front wheel on the right side. The second outlet port 28 b is connected, by an eighth piping tube 22 h, with a wheel cylinder 32RL of a disk brake mechanism 30 b provided at the rear wheel on the left side. The third outlet port 28 c is connected, by a ninth piping tube 22 i, with a wheel cylinder 32RR of a disk brake mechanism 30 c provided at the rear wheel on the right side. The fourth outlet port 28 d is connected, by a tenth piping tube 22 j, with a wheel cylinder 32FL of a disk brake mechanism 30 d provided at the front wheel on the left side.

In this case, brake fluid is supplied through the piping tubes 22 g-22 j connected with the respective outlet ports 28 a-28 d to the respective wheel cylinders 32FR, 32RL, 32RR, and 32FL of the disk brake mechanisms 30 a-30 d. A rise in the fluid pressure in the wheel cylinders 32FR, 32RL, 32RR, or 32FL operates the wheel cylinders 32FR, 32RL, 32RR, or 32FL, and a braking force is applied to the corresponding wheel (the right-side front wheel, the left-side rear wheel, the right-side rear wheel, or the left-side front wheel).

The vehicle brake system 10 is arranged to be mountable on various vehicles including, for example, a vehicle driven only by an engine (internal combustion engine), a hybrid vehicle, an electric vehicle, and a fuel cell vehicle.

The input device 14 includes a tandem master cylinder 34 capable of generating a fluid pressure by a driver's (operator's) operation of the brake pedal 12 and a first reservoir 36 provided at the master cylinder 34. Inside a cylinder tube 38 of the master cylinder 34, two pistons 40 a and 40 b are slidably arranged, wherein the two pistons 40 a and 40 b are separated from each other with a certain distance along the axial direction of the cylinder tube 38. The one piston 40 a is disposed adjacent to the brake pedal 12 and is connected with the brake pedal 12 through a push rod 42 to be directly moved. The other piston 40 b is disposed with a longer distance than the piston 40 a from the brake pedal 12.

A pair of piton packings 44 a and 44 b are respectively attached to the outer circumferential surfaces of the one and the other pistons 40 a and 40 b through an annular stepped portion. Back chambers 48 a and 48 b communicated with later-described supply ports 46 a and 46 b are formed between the pair of packings 44 a and 44 b. Further, a spring member 50 a is arranged between the one and the other pistons 40 a and 40 b. Another spring member 50 b is arranged between the other piston 40 b and the side end portion of the cylinder tube 38. Incidentally, the pair of piston packings 44 a and 44 b may be attached to the inner wall side of the cylinder tube 38 through an annular groove.

The cylinder tube 38 of the master cylinder 34 is provided with two supply ports 46 a and 46 b, two relief ports 52 a and 52 b, and two output ports 54 a and 54 b. In this case, the respective supply ports 46 a (46 b), and the respective relief ports 52 a (52 b), are arranged to respectively join with each other and communicate with a reservoir chamber, not shown, in the first reservoir 36.

Further, inside the cylinder tube 38 of the master cylinder 34, a first pressure chamber 56 a and a second pressure chamber 56 b are provided to generate a brake hydraulic pressure corresponding to a braking effort applied by the driver to the brake pedal 12. The first pressure chamber 56 a is arranged such as to communicate with the connection port 20 a through a first hydraulic passage 58 a. The second pressure chamber 56 b is arranged such as to communicate with the other connection port 20 b through a second hydraulic passage 58 b.

A pressure sensor Pm is provided between the master cylinder 34 and the connection port 20 a and on the upstream side of the first hydraulic passage 58 a. A first shut-off valve 60 a of a solenoid valve of a normally open type is provided on the downstream side of the first hydraulic passage 58 a. This pressure sensor Pm detects the fluid pressure on the upstream side, which is on a side of the master cylinder 34 of the first shut-off valve 60 a, on the first hydraulic passage 58 a.

Between the master cylinder 34 and the other connection port 20 b, a second shut-off valve 60 b of a solenoid valve of a normally open type is arranged on the upstream side from the second hydraulic passage 58 b, and a pressure sensor Pp is arranged on the downstream side from the second hydraulic passage 58 b. On the second hydraulic passage 58 b, this pressure sensor Pp detects the fluid pressure on the downstream side from the second shut-off valve 60 b, in other words, on the side of the wheel cylinders 32FR, 32RL, 32RR, and 32FL with respect to the second shut-off valve 60 b.

The normal openness of the first shut-off valve 60 a and the second shut-off valve 60 b refers to the type of a valve configured such that the normal position (the position of the valve body when current is not applied) is in a state of being at an open position (always open). Incidentally, in FIG. 1, the first shut-off valve 60 a and the second shut-off valve 60 b are shown in a close state in which a current is applied to the solenoids, and the valve bodies, not shown, are thereby operating.

At a point between the master cylinder 34 and the second shut-off valve 60 b, the second hydraulic passage 58 b is provided with a branched hydraulic passage 58 c branching from the second hydraulic passage 58 b. Serially connected to the branched hydraulic passage 58 c are a third shut-off valve 62 of a solenoid valve of a normally close type and a stroke simulator 64. The normal closing of the third shut-off valve 62 refers to the type of a valve configured such that the normal position (the position of the valve body when current is not applied) is in a state of being at a closed position (always closed). Incidentally, in FIG. 1, the third shut-off valve 62 is shown in a valve open state in which a current is applied to the solenoid, and the valve body, not shown, is thereby operating.

The stroke simulator 64 is a device that makes an operator feel as if a braking force were generated by a braking effort, by generating a stroke and a reaction force of the brake during by-wire control. The stroke simulator 64 is disposed on the second hydraulic passage 58 b and on a side of the master cylinder 34 of the second shut-off valve 60 b. The stroke simulator 64 is provided with a hydraulic pressure chamber 65 communicating with the branched hydraulic passage 58 c, and is arranged such as to be able to suck brake fluid let out through the hydraulic pressure chamber 65 from the second pressure chamber 56 b of the master cylinder 34.

Further, the stroke simulator 64 includes a first return spring 66 a with a larger spring constant, a second return spring 66 b with a smaller spring constant, the first and the second springs 66 a and 66 b being serially disposed with each other, and a simulator piston 68 pressurized by the first and second return springs 66 a and 66 b. The stroke simulator 64 is arranged such that the increase gradient of the pedal reaction force is set low during an early stage of pedaling the brake pedal 12, and the pedal react ion force is set high during a later stage of pedaling, so that the pedal feeling of the brake pedal 12 becomes equivalent to an existing master cylinder.

The configuration of the hydraulic passages is roughly categorized into a first fluid pressure system 70 a that connects the first pressure chamber 56 a of the master cylinder 34 and the plurality of wheel cylinders 32FR and 32RL, and a second fluid pressure system 70 b that connects the second pressure chamber 56 b of the master cylinder 34 and the plurality of wheel cylinders 32RR and 32FL.

The first fluid pressure system 70 a is configured by the first hydraulic passage 58 a connecting the output port 54 a of the master cylinder 34 (cylinder tube 38) of the input device 14 and the connection port 20 a, the piping tubes 22 a and 22 b connecting the connection port 20 a of the input device 14 and the output port 24 a of the motor cylinder device 16, the piping tubes 22 b and 22 c connecting the output port 24 a of the motor cylinder device 16 and the inlet port 26 a of the VSA device 18, and the piping tubes 22 g and 22 h connecting the outlet ports 28 a and 28 b of the VSA device 18 and the respective wheel cylinders 32FR and 32RL.

The second fluid pressure system 70 b includes the second hydraulic passage 58 b connecting the output port 54 b of the master cylinder 34 (cylinder tube 38) of the input device 14 and the other connection port 20 b, the piping tubes 22 d and 22 e connecting the other connection port 20 b of the input device 14 and the output port 24 b of the motor cylinder device 16, the piping tubes 22 e and 22 f connecting the output port 24 b of the motor cylinder device 16 and the inlet port 26 b of the VSA device 18, and the piping tubes 22 i and 22 j for connecting the outlet ports 28 c and 28 d of the VSA device 18 and the respective wheel cylinders 32RR and 32FL.

As a result, because the hydraulic passages are formed with the first fluid pressure system 70 a and the second fluid pressure system 70 b, the respective wheel cylinders 32FR and 32RL, and the respective wheel cylinders 32RR and 32FL, can be independently operated so that braking forces which are independent from each other can be generated.

FIG. 2 is a perspective view of the motor cylinder device shown in FIG. 1. FIG. 3 is a side view of the motor cylinder device. FIG. 4 is an exploded perspective view of the motor cylinder device. FIG. 5 is an exploded perspective view of a driving force transmission section constructing the motor cylinder device. FIG. 6 is an exploded perspective view of a cylinder mechanism constructing the motor cylinder device.

The motor cylinder device 16 that functions as an electric brake actuator includes, as shown in FIG. 2, an actuator mechanism 74 having an electric motor 72 and a driving force transmission section 73, and a cylinder mechanism 76 driven by the actuator mechanism 74. In this case, as shown in FIG. 4, the electric motor 72, the driving force transmission section 73, and the cylinder mechanism 76 are arranged to be separable from each other.

Further, the driving force transmission section 73 of the actuator mechanism 74 includes a gear mechanism (decelerating mechanism) 78 for transmitting the rotational driving force of the electric motor 72, and a ball screw assembly (conversion mechanism) 80 that converts this rotational driving force into linear movement (axial force along a linear direction) and transmits the linear movement to a side of a later-described slave pistons 88 a and 88 b of the cylinder mechanism 74.

The electric motor 72 is subjected to drive control, based on a control signal (electric signal) from control means, not shown. The electric motor 72 is, for example, a servomotor and is disposed above the actuator mechanism 74. Accordingly, it can be favorably avoided that oil component, such as grease, in the driving force transmission section 73 enters inside the electric motor 72 by gravity action.

The electric motor 72 is configured with a motor casing 72 a formed in a sleeve shape having a bottom and a base portion 72 b to which a harness, not shown, is connected, the base portion 72 b being integrally joined with the motor casing 72 a. The base portion 72 b is provided with a plurality of insertion holes 77 b which screw members 77 a penetrate through, and the electric motor 72 is fastened to a later-described actuator housing 75 through the screw members 77 a.

The driving force transmission section 73 has the actuator housing 75, and mechanical elements, such as the gear mechanism (deceleration mechanism) 78 and the ball screw assembly (conversion mechanism) 80, for driving force transmission are housed in the space portion inside the actuator housing 75. As shown in FIG. 5, the actuator housing 75 has a structure that can be divided into a first body 75 a disposed on a side of the cylinder mechanism 76 and a second body 75 b that closes an opening end on the side opposite to the cylinder mechanism 76 with respect to the first body 75 a.

As shown in FIG. 4, a pair of screw holes 77 c is provided on the upper side of the first body 75 a to mount the electric motor 72 to the driving force transmission section 73, and the electric motor 72 is fixed by fastening the pair of the screws 77 a to the screw holes 77 c. Further, a flange portion 79 substantially in a rhombic shape is provided at the end portion of the first body 75 a on a side of the cylinder mechanism 76, and a pair of screw holes 81 c is provided at the flange portion 79 to fit an opening portion 79 a substantially in a circular shape and the cylinder mechanism 76. In this case, a pair of screw members 81 a penetrating through insertion holes 81 b of a flange portion 82 a provided on the other end of a later-described cylinder main body 82 are screw-engaged with the screw holes 81 c, and the cylinder mechanism 76 and the driving force transmission section 73 are thereby integrally joined.

As shown in FIG. 5, the gear mechanism 78 and the ball screw assembly 80 are housed between the first body 75 a and the second body 75 b. The gear mechanism 78 includes a pinion gear 78 a (see FIG. 1) being in a small diameter and engaged with the output shaft of the electric motor 72, an idle gear 78 b in a small diameter engaging with the pinion gear 78 a, and a ring gear 78 c in a large diameter engaging with the idle gear 78 b.

The ball screw assembly 80 includes: a ball screw shaft 80 a whose one end is joined with the first slave piston 88 a of the cylinder mechanism 76; a plurality of balls 80 b (see FIG. 1) that rollingly move along a thread groove in a scrolled shape formed on the outer circumferential surface of the ball screw shaft 80 a; a nut member 80 c that is substantially in a sleeve shape, fitted inside the ring gear 78 c to integrally rotate with the ring gear 78 c, and threadly engaged with the balls 80 b; and a pair of ball bearings 80 d that rotatably and axially support the one end side and the other end side of the nut member 80 c along the axial direction. Incidentally, the nut member 80 c is fixed to the inner diameter surface of the ring gear 78 c, for example, by pressure fitting.

The driving force transmission section 73 is configured as described above and thus, after the rotational driving force of the electric motor 72 transmitted through the gear mechanism 78 is input to the nut member 80 c, the driving force transmission section 73 converts, by the ball screw assembly 80, the driving force into a linear axial force (linear movement) to have a forward and backward motion to cause the ball screw shaft 80 a to move along the axial direction.

The first body 75 a and the second body 75 b of the actuator housing 75 are arranged such as to be integrally joined through four bolts 83 a and also to be separable from each other. The first body 75 a is provided with insertion holes 83 b through which the four bolts 83 a penetrate, and the second body 75 b is provided with screw holes 83 c at positions corresponding to the insertion holes 83, wherein the thread portions of the bolts 83 a are screw-inserted in the screw holes 83 c.

In this case, the thread portions of the bolts 83 a penetrating through the insertion holes 83 b of the first body 75 a are screw-inserted into the screw holes 83 c of the second body 75 b, and the first body 75 a and the second body 75 b are thereby integrally fastened. Incidentally, a circular recession 85 b is provided on the upper side of the second body second body 75 b, and a bearing 85 a is attached to the circular recession 85 b to axially and rotatably support the tip end portion of the output shaft of the electric motor 72.

In the present embodiment, with a plane that is substantially perpendicular to the axial line A of the cylinder main body 82 of the cylinder mechanism 76 as a dividing plane F (see FIG. 4), the actuator housing 75 has a divided structure with the first body 75 a and the second body 75 b, and the fastening direction of the plural bolts 83 a (see FIG. 5) are thus parallel to the axial line A of the cylinder main body 82. As a result, in the present embodiment, the fitting task can be easily carried out.

The cylinder mechanism (cylinder) 76 includes the cylinder main body 82 in a cylindrical shape with a bottom and a second reservoir 84 arranged at the cylinder main body 82. The second reservoir 84 is connected by a piping tube 86 with the first reservoir 36 arranged at the master cylinder 34 of the input device 14. Brake fluid reserved in the first reservoir 36 is supplied to the second reservoir 84 through the piping tube 86.

As shown in FIG. 1 and FIG. 6, the first slave piston (piston) 88 a and the second slave piston (piston) 88 b are slidably arranged inside the cylinder main body 82, wherein the slave pistons 88 a and 88 b are separated from each other with a certain distance along the axial direction of the cylinder main body 82. The first slave piston 88 a is disposed adjacent to a side of the ball screw assembly 80, is in contact with one end portion of the ball screw shaft 80 a through a connection hole 89, and is displaced in the direction arrow X1 or X2 integrally with the ball screw shaft 80 a. The second slave piston 88 b is disposed farther than the slave piston 88 a from a side of the ball screw assembly 80.

A pair of slave piston packings 90 a and 90 b are attached on the outer circumferential surfaces of the first and second slave pistons 88 a and 88 b through an annular stepped portion. A first back chamber 94 a and a second back chamber 94 b are formed (see FIG. 1), which are respectively communicated with later-described reservoir ports 92 a and 92 b, are formed between the pair of the slave piston packings 90 a and 90 b. Further, a first return spring 96 a is arranged between the first and second slave pistons 88 a and 88 b, and a second return spring 96 b is arranged between the second slave piston 88 b and the side end portion (bottom wall) of the cylinder main body 82.

The cylinder main body 82 of the cylinder mechanism 76 is provided with the two reservoir ports 92 a and 92 b and the two output ports 24 a and 24 b. In this case, the reservoir port 92 a (92 b) is arranged such as to communicate with a reservoir chamber, not shown, in the second reservoir 84.

A first hydraulic pressure chamber 98 a is provided in the cylinder main body 82 to control the brake hydraulic pressure that is output from the output port 24 a to a side of the wheel cylinders 32FR and 32RL. Further, a second hydraulic pressure chamber 98 b is provided in the cylinder main body 82 to control the brake hydraulic pressure that is output from the other output port 24 b to a side of the wheel cylinders 32RR and 32FL.

Restricting means 100 in a bolt shape is provided between the first slave piston 88 a and the second slave piston 88 b to restrict the maximum stroke (the maximum displacement distance) and the minimum stroke (the minimum displacement distance) of the slave piston 88 a and the slave piston 88 b. Further, the second slave piston 88 b is provided with a stopper pin 102 that engages with a penetration hole 91 penetrating along a direction substantially perpendicular to the axial line of the second slave piston 88 b, restricts the sliding range of the second slave piston 88 b, and inhibits over return of the slave piston 88 b to a side of the slave piston 88 a. The restricting means 100 and the stopper pin 102 prevent a defect of another system at the time of a defect of one system, particularly at the time of backup when braking is carried out by a brake hydraulic pressure generated by the master cylinder 34.

Incidentally, as shown in FIG. 6, a piston guide 103 engagedly stopped by a circlip, not shown, is attached to the opening portion of the cylinder main body 82. This piston guide 103 is provided with a through hole 103 a thorough which the first piston 88 a can penetrate with a clearance. By sliding the rod portion of the first piston 88 a along the piston guide 103, the first piston 88 a in contact with one end portion of the ball screw shaft 80 a can be linearly guided. Further, a connection piston 105 is connected to the second piston 88 b. The connection piston 105 is provided with an engagement hole, not shown, with which a head portion 100 a of the restricting means 100 formed in a bolt shape engages.

FIG. 7 is a perspective view of the motor cylinder device in a view from below. FIG. 8 is a perspective view showing a state that the motor cylinder device is fixed to a vehicle body frame through a mount portion.

As shown in FIG. 7, a mount portion 111 is provided on the lower side of the actuator housing 75 (the first body 75 a) to mount the motor cylinder device 16 to the vehicle body frame. This mount portion 111 includes a first boss portion 113 a, a second boss portion 113 b, and a third boss portion 115, and is stably supported at three points. The first boss portion 113 a is disposed on the left side in a view from a side of the second body 75 b, and is arranged such as to protrude in the direction substantially perpendicular to the axial line of the cylinder main body 82. The second boss portion 113 b is disposed on the right side in a view from a side of the second body 75 b, and is arranged such as to protrude in the direction opposite to the first boss portion 113 a. The third boss portion 115 is formed in a shape protruding downward in a view from a side of the second body 75 b. The first boss portion 113 a, the second boss portion 113 b, and the third boss portion 115 are provided with respective mount holes 117. The first boss portion 113 a, the second boss portion 113 b, and the third boss portion 115 are formed integrally with the first body 75 a, for example, by die-casting using a light metal material, such as an aluminum alloy.

As shown in FIG. 8, the motor cylinder device 16 is fitted through a fitting bracket 119 to the vehicle body, for example, at a front side frame 121 of the vehicle body.

This fitting bracket 119 is formed by a bottom plate 119 c having a protruding portion 123 that is attached to the mount hole 117 of the third boss portion 115, and a pair of side plates 119 a and 119 b that support the first boss portion 113 a and the second boss portion 113 b of the motor cylinder device 16, sandwiching them in the left-right horizontal direction. The pair of the side plates 119 a and 119 b are provided with respective engaging-stop portions 127 to engagingly stop screw members 125 which are respectively inserted in the mount holes 117 of the first boss portion 113 a and the second boss portion 113 b. Incidentally, buffing members 129 are intermediately arranged respectively between the side plate 119 a and the screw member 125, between the side plate 119 b and the screw member 125, and between the protruding portion 123 of the a bottom plate 119 c and the third boss portion 115.

Returning to FIG. 1, the VSA device 18 includes a generally known component and includes a first brake system 110 a for control of the first fluid pressure system 70 a connected to the disk brake mechanisms 30 a and 30 b (wheel cylinders 32FR and 32RL) for the right-side front wheel and the left-side rear wheel. Further, the VSA device 18 includes a second brake system 110 b for control of the second fluid pressure system 70 b connected to the disk brake mechanisms 30 c and 30 d (wheel cylinders 32RR and 32FL) for the right-side rear wheel and the left-side front wheel.

Incidentally, the first brake system 110 a may be formed by a fluid pressure system connected to the disk brake mechanisms arranged at the left-side front wheel and the right-side front wheel, and the second brake system 110 b may be formed by a fluid pressure system connected to the disk brake mechanisms arranged at the left-side rear wheel and the right-side rear wheel. Further, the first brake system 110 a may be formed by a fluid pressure system connected to the disk brake mechanisms arranged at the right-side front wheel and the right-side rear wheel on one side of the vehicle body, and the second brake system 110 b may be formed by a fluid pressure system connected to the disk brake mechanisms arranged at the left-side front wheel and the left-side rear wheel on the other one side of the vehicle body.

As the first brake system 110 a and the second brake system 110 b have the same structure, elements corresponding between the first brake system 110 a and the second brake system 110 b are designated with the same reference symbols. In the following, the first brake system 110 a will be mainly described while describing the second brake system 110 b with bracketed notes.

The first brake system 110 a (the second brake system 110 b) has a first shared hydraulic passage 112 and a second shared hydraulic passage 114 shared by the wheel cylinders 32FR and 32RL (32RR and 32FL). The VSA device 18 includes a regulator valve 116, which is a normal-open type solenoid valve disposed between the inlet port 26 a and the first shared hydraulic passage 112, a first check valve 118 that is arranged in parallel with the regulator valve 116 to allow the brake fluid to flow from a side of the inlet port 26 a to a side of the first shared hydraulic passage 112 (while inhibiting the brake fluid from flowing from a side of the first shared hydraulic passage 112 to a side of the inlet port 26 a), and a first invalve 120, which is a normally open type solenoid valve disposed between the first shared hydraulic passage 112 and the first outlet port 28 a. Further, the VSA device 18 includes a second check valve 122 that allows the brake fluid to flow from a side of the first outlet port 28 a to a side of the first shared hydraulic passage 112 (while inhibiting the brake fluid from flowing from the side of the first shared hydraulic passage 112 to a side of the first outlet port 28 a), the second check valve 122 being arranged parallel with the first invalve 120, a second invalve 124, which is a normally open type solenoid valve disposed between the first shared hydraulic passage 112 and the second outlet port 28 b, and a third check valve 126 that allows the brake fluid to flow from a side of the second outlet port 28 b to the side of the first shared hydraulic passage 112 (while inhibiting the brake fluid from flowing from the side of the first shared hydraulic passage 112 to the second outlet port 28 b side), the third check valve 126 being arranged parallel to the second invalve 124.

Still further, the VSA device 18 includes a first outvalve 128, which is a normally closed type solenoid valve disposed between the first outlet port 28 a and the second shared hydraulic passage 114, a second outvalve 130, which is a normally closed type solenoid valve disposed between the second outlet port 28 b and the second shared hydraulic passage 114, a reservoir 132 connected to the second shared hydraulic passage 114, a fourth check valve 134 that is disposed between the first shared hydraulic passage 112 and the second shared hydraulic passage 114 to allow the brake fluid to flow from a side of the second shared hydraulic passage 114 to the side of the first shared hydraulic passage 112 (while inhibiting the brake fluid from flowing from the side of the first shared hydraulic passage 112 to the side of the second shared hydraulic passage 114), a pump 136 that is disposed between the fourth check valve 134 and the first shared hydraulic passage 112 to supply the brake fluid from the side of the second shared hydraulic passage 114 to the side of the first shared hydraulic passage 112, a suction valve 138 and a discharge valve 140 provided before and after the pump 136, a motor M for driving the pump 136, and a suction valve 142 disposed between the second shared hydraulic passage 114 and the inlet port 26 a.

Incidentally, in the first brake system 110 a, a pressure sensor Ph is provided on the hydraulic passage adjacent to the inlet port 26 a to detect the brake hydraulic pressure having been output from the output port 24 a of the motor cylinder device 16 and controlled by the first hydraulic pressure chamber 98 a of the motor cylinder device 16. Detection signals detected by the respective pressure sensors Pm, Pp, and Ph are introduced to control means, not shown. Further, the VSA device 18 includes a function to perform ABS control in addition to VSA control.

The vehicle brake system 10, in which the motor cylinder device 16 in the present embodiment is built, is basically configured as described above. The operation and advantages of the vehicle brake system 10 will be described below.

During normal operation when the vehicle brake system 10 normally functions, the first shut-off valve 60 a and the second shut-off valve 60 b, which are normally open type, are magnetically excited by applying current and thereby turn into a valve close state, and the third shut-off valve 62, which is a normally closed type solenoid valve, is excited by applying current and thereby turns into a valve open state. Accordingly, as the first fluid pressure system 70 a and the second fluid pressure system 70 b are shut off by the first shut-off valve 60 a and the second shut-off valve 60 b, it does not occur that a brake hydraulic pressure generated by the master cylinder 34 of the input device 14 is transmitted to the wheel cylinders 32FR, 32RL, 32RR, and 32FL of the disk brake mechanisms 30 a-30 d.

At this moment, a brake hydraulic pressure generated by the second pressure chamber 56 b of the master cylinder 34 is transmitted through the branched hydraulic passage 58 c and the third shut-off valve 62 in the valve open state to the hydraulic pressure chamber 65 of the stroke simulator 64. The brake hydraulic pressure supplied to the hydraulic pressure chamber 65 displaces the simulator piston 68 against the spring forces of the springs 66 a and 66 b, and a stroke of the brake pedal 12 is thereby allowed and a pseudo petal reaction force is generated to be applied to the brake pedal 12. As a result, a brake feeling without a strange feeling for a driver can be obtained.

In such a system state, when the control means, not shown, has detected pedaling of the brake pedal 12 by the driver, the control means drives the electric motor 72 of the motor cylinder device 16 to urge the actuator mechanism 74, and displaces the first slave piston 88 a and the second slave piston 88 b toward the direction arrow X1 in FIG. 1 against the spring forces of the first return spring 96 a and the second return spring 96 b. By the displacements of the first slave piston 88 a and the second slave piston 88 b, the brake hydraulic pressures inside the first hydraulic pressure chamber 98 a and the second hydraulic pressure chamber 98 b are increased, balancing with each other, and a desired brake hydraulic pressure is thus generated.

These brake hydraulic pressures of the first hydraulic pressure chamber 98 a and the second hydraulic pressure chamber 98 b in the motor cylinder device 16 are transmitted through the first invalve 120 and the second invalve 124 of the VSA device 18 which are in the valve open state, to the wheel cylinders 32FR, 32RL, 32RR, and 32FL of the disk brake mechanisms 30 a-30 d. By operation of the wheel cylinders 32FR, 32RL, 32RR, and 32FL, desired braking forces are applied to the respective wheels.

In other word, by the vehicle brake system 10 in the present embodiment, during a normal state when the motor cylinder device 16, which functions as a dynamic fluid pressure source, an ECU, not shown, and the like for by-wire control are operable, a so-called brake by-wire type brake system becomes active wherein in a state that communication between the master cylinder 34, which generates a brake hydraulic pressure by an operator's pedaling of the brake pedal 12, and the disk brake mechanisms 30 a-30 d (wheel cylinders 32FR, 32RL, 32RR, an 32FL) that brake the respective wheels are shut off by the first shut-off valve 60 a and the second shut-off valve 60 b, the disk brake mechanisms 30 a-30 d are operated by the brake hydraulic pressure generated by the motor cylinder device 16. Accordingly, the present embodiment can be suitably applied to a vehicle, such as an electric vehicle or the like, in which a negative pressure that could be caused by a conventional internal combustion engine does not exist.

On the other hand, during an abnormal state when the motor cylinder device 16 or the like is inoperable, a so-called conventional hydraulic type brake system becomes active, wherein the first shut-off valve 60 a and the second shut-off valve 60 b are respectively made in a valve open state, and the third shut-off valve 62 is made in a valve close state so as to transmit a brake hydraulic pressure generated by the master cylinder 34 to the disk brake mechanisms 30 a-30 d (wheel cylinders 32FR, 32RL, 32RR, 32FL) and thereby operate the disk brake mechanisms 30 a-30 d (wheel cylinders 32FR, 32RL, 32RR, and 32FL).

In the present embodiment, the motor cylinder device 16 is constructed by three members that are the cylinder mechanism 76 provided with the first and second slave pistons 88 a and 88 b for generating a brake hydraulic pressure, the electric motor 72, and the actuator housing 75 formed such as to house the gear mechanism 78 and the ball screw assembly 80 and to be separable from the cylinder mechanism 76. As a result, in the present embodiment, a desired brake pressure can be generated with a simple structure, and for example, it is possible to independently produce any of the three members, so that the entire device can be downsized and the versatility can be improved.

Further, in the present embodiment, the actuator housing 75 is supported by providing the mount portion 111 at the actuator housing 75 (the first body 75 a), and the actuator housing 75 can thus be easily fitted to the vehicle body frame, for example, at the front side frame 121 or the like of the vehicle body frame.

Still further, in the present embodiment, with a plane that is substantially perpendicular to the axial line A of the cylinder main body 82 of the cylinder mechanism 76 as a dividing plane F (see FIG. 4), the actuator housing 75 has a divided structure with the first body 75 a and the second body 75 b, and the fastening direction of the plural bolts 83 a is thus parallel to the axial line A of the cylinder main body 82. As a result, the fitting task can be easily carried out.

Incidentally, in the present embodiment, it is possible to obtain a vehicle brake system 10 provided with the motor cylinder device 16 that is capable of generating a desired brake pressure with a simple structure and enables downsizing of the entire device and improvement in the versatility. This vehicle can be, for example, a four wheel drive vehicle (4WD), a front wheel drive vehicle (FF), a rear wheel drive vehicle (FR), or the like.

DESCRIPTION OF REFERENCE SYMBOLS

-   10 . . . vehicle brake system -   16 . . . motor cylinder device (electric brake actuator) -   72 . . . electric motor -   75 . . . actuator housing -   75 a . . . first body -   75 b . . . second body -   76 . . . cylinder mechanism (cylinder) -   78 . . . gear mechanism -   80 . . . ball screw assembly (conversion mechanism) -   88 a, 88 b . . . slave piston (piston) -   98 a, 98 b . . . hydraulic pressure chamber -   111 . . . mount portion 

The invention claimed is:
 1. An electric brake system, comprising: a master cylinder configured to generate a master cylinder pressure according to a braking operation by a driver, and generate a brake hydraulic pressure, based on an electric signal according to the braking operation; and an electric brake actuator that is communicated and connected with the master cylinder, the electric brake actuator comprising: a cylinder mechanism provided with a piston that is displaced along a hydraulic pressure chamber: an electric motor configured to drive the piston; and an actuator housing formed separable from the cylinder mechanism, wherein the actuator housing houses a gear mechanism configured to transmit a rotational driving force of the electric motor, and a conversion mechanism configured to convert the rotational driving force transmitted through the gear mechanism, into a linear movement and transmit the linear movement to the piston, wherein the actuator housing includes a mount portion configured to mount the electric brake actuator to a vehicle, wherein the mount portion comprises: a first boss portion and a second boss portion protruding toward left and right sides in a direction substantially perpendicular to an axial line of the cylinder mechanism; and a third boss portion protruding downward from the cylinder mechanism and perpendicular to the first and second boss portions.
 2. The electric brake actuator according to claim 1, wherein the actuator housing is configured to be divisible in two, on a plane substantially orthogonal with an axial line of the cylinder as a dividing plane.
 3. A brake system for a vehicle, provided with an electric brake actuator that is communicated and connected with a master cylinder configured to generate a master cylinder pressure according to a braking operation by a driver, and generate a brake hydraulic pressure, based on an electric signal according to the braking operation, the electric brake actuator comprising: a cylinder mechanism provided with a piston that is displaced along a hydraulic pressure chamber: an electric motor configured to drive the piston; and an actuator housing formed separable from the cylinder mechanism, wherein the actuator housing houses a gear mechanism configured to transmit a rotational driving force of the electric motor, and a conversion mechanism configured to convert the rotational driving force transmitted through the gear mechanism, into a linear movement and transmitting the linear movement to the piston, wherein the actuator housing includes a mount portion configured to be mounted to allow the electric brake actuator to be supported, wherein the mount portion comprises: a first boss portion and a second boss portion protruding toward left and right sides in a direction substantially perpendicular to an axial line of the cylinder mechanism; and a third boss portion protruding downward from the cylinder mechanism and perpendicular to the first and second boss portions. 